1. Field of the Invention
This invention relates to a variable power optical system suited to installation in a compact digital still camera (digital camera), a consumer video camera, etc.
2. Description of Related Art
To take a photograph with a digital camera, a consumer video camera, etc., if vibration is caused by hand movement of the photographer or for any other reason, blurring of the photograph image occurs, resulting in degradation of the image. To prevent such image blurring, hitherto, a method of moving some lens of a photograph optical system in the perpendicular direction to the optical axis as a correction lens group and optically correcting image blurring has been known. (For example, refer to Japanese Patent Nos. 2535969, 2560377 and 2605326.)
Japanese Patent No. 2535969 discloses a variable power optical system including a first lens group I fixed at the variable power time and a second lens group II and a third lens group III moving along the optical axis at the variable power time wherein any one of the first lens group I to the third lens group III is moved in the direction orthogonal to the optical axis, thereby correcting blurring of a photograph image accompanying vibration, for example, as shown in FIG. 4 of the patent.
Japanese Patent No. 2560377 discloses a variable power optical system including a negative first lens group I fixed at the variable power time and a positive second lens group II and a negative third lens group III moving along the optical axis at the variable power time wherein the second lens group II is moved in the direction orthogonal to the optical axis, thereby correcting blurring of a photograph image accompanying vibration, for example, as shown in FIG. 4 of the patent.
Japanese Patent No. 2605326 discloses a variable power optical system including a negative first lens group I fixed at the variable power time and a positive second lens group II and a negative third lens group III moving along the optical axis at the variable power time wherein the third lens group III is moved in the direction orthogonal to the optical axis, thereby correcting blurring of a photograph image accompanying vibration, for example, as shown in FIG. 4 of the patent.
Further, JP-A-2006-23593 discloses a zoom lens including a positive first lens group G1, a negative second lens group G2 moving along the optical axis at the variable power time, a positive third lens group G3, a positive fourth lens group G4 moving along the optical axis at the variable power time, and a positive fifth lens group G5 in order wherein a positive partial group of some lens of the fifth lens group G5 is shifted in the direction orthogonal to the optical axis, thereby shifting an image, for example, as shown in FIG. 2 of the publication.
However, in the variable power optical systems in the patents described above, the occupation ratio of the lens group for making image blurring correction (which will be hereinafter referred to as correction lens group) to the overall configuration is comparatively large and thus electric and mechanical loads on the drive section for driving the correction lens group are not small and in addition, it is disadvantageous for compacting the overall configuration. Particularly, if the correction lens group also functions as a variable power group for performing the variable power operation, the load on the drive section particularly grows and in addition, the mechanism also easily becomes complicated. Since the lenses (group) preceding and following the correction lens group are a variable power group for performing the variable power operation, it is difficult to enhance the sealing performance because of the mechanism and it is feared that foreign material of dust, etc., may enter the inside and be deposited. Particularly, if the last lens group (lens group nearest to the image side) is a variable power group and is a moving group as in the variable power optical system in Japanese patent No. 2605326, dust is easily deposited on the last lens group, in which case the effect of shading appears in the photograph image.
In the zoom lens in JP-A-2006-23593 described above, the overall length tends to become long and compactibility is insufficient.